Did a Democratic member of Congress improperly enlist the support of a major pro-Israel lobbying group to try to win a top committee assignment? That's the question at the heart of an ongoing investigation by the FBI and Justice Department prosecutors, who are examining whether Rep. Jane Harman of California and the American Israel Public Affairs Committee (AIPAC) may have violated the law in a scheme to get Harman reappointed as the top Democrat on the House intelligence committee, according to knowledgeable sources in and out of the U.S. government.

The sources tell TIME that the investigation by Justice and the Federal Bureau of Investigation, which has simmered out of sight since about the middle of last year, is examining whether Harman and AIPAC arranged for wealthy supporters to lobby House Democratic leader Nancy Pelosi on Harman's behalf. Harman said Thursday in a voicemail message that any investigation of  or allegation of improper conduct by  her would be "irresponsible, laughable and scurrilous." On Friday, Washington GOP super lawyer Ted Olson left voicemail messages underscoring that Harman has no knowledge of any investigation. "Congresswoman Harman has asked me to follow up on calls you've had," Olson said. "She is not aware of any such investigation, does not believe that it is occurring, and wanted to make sure that you and your editors knew that as far as she knows, that's not true... . No one from the Justice Department has contacted her." It is not, however, a given that Harman would know that she is under investigation. In a follow-up phone call from California, Olson said Harman hired him this morning because she takes seriously the possibility of a media report about an investigation of her, even though she does not believe it herself.

A spokesman for AIPAC, a powerful Washington-based organization with more than 100,000 members across the U.S., denied any wrongdoing by the group and stressed that it is not taking sides in regards to the committee assignment. Spokespersons for Justice and the FBI declined to comment.